Amino-functional polysiloxanes are generally known. Commonly the aminoalkyl functional groups are attached to the silicon atom in a terminal position, and comprise the structure of general formula (I).

Amino-functional polysiloxanes are commonly prepared by the platinum catalyzed hydrosilylation of allyl amine to a hydridosiloxane such as described in U.S. Pat. No. 5,026,890, U.S. Pat. No. 4,649,208, U.S. Pat. No. 5,892,084 and U.S. Pat. No. 6,177,583. In these processes, the aminopropylpolysiloxanes are often obtained with highly colored impurities. These impurities can include, among others, iminoalkyl functional groups of the general formula (IV).
wherein Ra is commonly hydrogen and Rb is commonly a C2-C5, optionally branched and/or unsaturated alkyl group (cf. comparative examples 4 and 5 below), and wherein each R1 group is independently selected from the group consisting of a monovalent C1-C20 alkyl, arylalkyl, alkylaryl, and aryl group, each of them being linear or branched, each R2 group is independently selected from the group consisting of linear or branched divalent optionally substituted organic radicals with 3 to 7 carbon atoms which can be interrupted by —O—, —NH—. The impurities of the general formula (IV) are commonly observed as uncontrolled byproducts of the hydrosilylation reaction with platinum at a level of about 2-about 10 mole-% of the total aminoalkyl-groups in the polymer. The impurities of the general formula (IV) are identified by signals in the proton NMR in the range of 7.4 to 7.7 ppm, and/or near 5.7, 3.31, 2.22, 1.8 and 1.50 ppm, among others. Moreover, there are also other byproducts in the above-mentioned process. For example, undesirable highly colored impurities are commonly identified by signals in the proton NMR in the range of 3.1 to 3.4 and near 4.0 ppm, among others.
These iminoalkyl impurities are detrimental in applications of these materials. In particular, linear aminopropyl polysiloxanes of formula (I) are employed to make linear polysiloxane-polyimide and polysiloxane-polyetherimide block copolymers.
U.S. Pat. No. 3,325,450 describes a process for making polysiloxane-polyimide block copolymers by reaction of aminopropyl-functional polysiloxanes of the general formula (I) and organic dianhydrides.
U.S. Pat. No. 4,586,997 describes a process for making polysiloxane-polyetherimide block copolymers by reaction of aminopropyl-functional polysiloxanes of the general formula (I) and organic bis(etheranhydrides) and organic diamines.
The iminoalkyl impurities of the general formula (IV) in these aminopropyl-functional polysiloxanes are unreactive in the synthesis of these block copolymer materials, and thus are undesirable chain-terminating groups, that lead to reduced block copolymer formation and poor control of molecular weight. Without wishing to be bound by theory, it is believed that the colored impurities include secondary amino-functional siloxanes that also function as undesirable chain-terminating groups in block copolymer synthesis. Likewise highly colored impurities lead to undesirable increased color in the resultant block copolymers.
Using the state-of-the art as described in '890, '208, '084 and '583 inevitably leads to impurities of the general formula (IV) (e. g. comparative examples 4 and 5 below). There is no known technology for avoiding these byproducts in the direct reactions of allyl amine with hydridosiloxanes under platinum catalysis.
Alternatively, it has been proposed to avoid the formation of impurities of the general formula (IV) by first protecting the primary amino function in allyl amine, then performing the hydrosilylation with the hydridosiloxane and platinum, followed then by deprotection of the amino function to give the final amino-functional polysiloxanes.
U.S. Pat. No. 4,584,393 describes the reaction of allyl amine with trimethylchlorosilane followed by purification by distillation to give the silazane
then reaction of this silazane with hydridosiloxanes under platinum catalysis and finally hydrolysis of the silazane group to form aminopropyl-functional polysiloxanes of formula (I). This process gives products that are, as a rule, highly colored.
GB Patent No. 2,185,984 describes formation of ketimines of allyl amine with simple ketones such as methylethylketone or cyclohexanone first, followed after by neutralization of the acid catalyst used by purification of the ketamine by distillation. This ketimine is then reacted under platinum catalysis with a hydridosiloxane. Finally, the ketimine group is removed by acid catalyzed hydrolysis. The acid catalyst used to remove the ketimine group is preferably acid activated clay.
The methods according to '393 and '984 have the disadvantage of employing reactions of the highly toxic allyl amine to produce intermediates requiring purification. This adds cost and unnecessary handling of toxic intermediates and byproducts. In addition, these methods do not provide for the removal of colored impurities that can form during hydrosilylation and subsequent manipulations.